1. Field of the Invention
The present invention relates to a vehicle lamp having a predetermined joint where a lamp body for forming the vehicle lamp such as an automobile signal lamp and a front lens for covering the front opening of the lamp body are directly joined together by a fusion-welding method. More particularly, the invention relates to a fusion-welding leg structure of a vehicle lamp in which a predetermined joint where the leg of a front lens and a lamp body are joined together is partially fused with the frictional heat generated by utilizing electromagnetic vibrations before being cooled in order to join both of them together.
2. Related Art
There has heretofore been proposed a vehicle lamp manufactured by the so-called vibration-fusion-welding method for joining together a lamp body 51 made of thermoplastic synthetic resin and a front lens 52 also made of thermoplastic synthetic resin, for example, by vibration-fusion-welding the predetermined joint between them for welding purposes as disclosed in FIGS. 7A and 7B. Such a vehicle lamp is manufactured according to this method comprising the steps of bringing the fusion-welding leg 54 of the front lens 52 into contact with the joint surface 53 of the flange portion of the lamp body of the vehicle lamp, causing frictional heat to be generated by vibrating both of them in the as-joined condition and fitting the fusion-welding leg 54 of the front lens 52 into the joint surface 53 of the lamp body 51. The fusion-welding leg 54 formed on the side of the front lens 52 is so formed as to have the same width vertically as shown in FIG. 7A (indicated by a double-headed arrow A) or otherwise to taper off in cross section to the leading end of the fusion-welding leg 54 as shown in FIG. 7B (indicated by an arrow B).
In the case of the fusion-welding leg 54 on the side of the front lens 54 formed as mentioned previously, the former shown in FIG. 7A, for example, has a wide contact surface with respect to the joint surface 53 on the side of the lamp body 51 and since satisfactory great pressure is not applied to both contact surfaces as a whole, the frictional heat is hardly easily generated and fusion-welding time is made longer thereby; the problem is that the production of burrs on the edge of the fusion-welding leg 54 tends to increase because the fusion welding is carried out at relatively low temperatures. On the other hand, the latter shown in FIG. 7B has the fusion-welding leg 54 having a tip narrow in width and though the fusion-welding time can be shortened because high frictional heat is attained, the production of burrs on the inside and outside edges of the lamp also increases; the problem in this case is that the production of burrs inward tends to deteriorate the illumination effect and the neatness of the external appearance of the lamp.